compton ave .. just north of washington blvd.. east side of the street.. might be able to help..

there are a LOT of shops around..

i am taking that the drive train has been changed and the 350 engine has a TH350, TH400, 700R4 in it..

do you still have all the clutch pedals and clutch bell cranks or you can convert it to hydraulic clutch.. do you have any parts at all... a transmission.. a bell housing.. flywheel.. clutch disc and cover.. proper flywheel to crank bolts.. proper clutch cover to flywheel bolts.. ready for a different starter.. if the flywheel size is different than the automatic... shifter that will clear your seats..

i am also taking that you have a later rear end.. that will handle the abuse a 4, 5, or 6 speed manual transmission can put out..

i am not trying to talk you out of it.. but .. it's a significant project...

a shift kit and checking out the stall speed of the torque converter.. depending on what you want to ***

if you are attempting to increase fuel economy... there are transmissions with lock up torque converters available.. there are also overdrive transmissions available..

a lot of fuel economy can be picked up by monitoring your air fuel ratio during idle.. idle transition.. the main circuits and the power enrichment circuit..